1. Field of the Invention
The present invention relates to a recording apparatus for performing the recording by discharging ink onto a recording medium. More particularly, the present invention relates to a fixater for expediting the fixation of ink discharged on the recording medium, and a recording apparatus in which the aforesaid fixater can be mounted detachably.
2. Related Background Art
Traditionally, an image recording apparatus such as a printer, copying machine, or facsimile apparatus is provided with a recording unit to form an image on paper, thin plastic plate, and other recording media in accordance with image information.
The aforesaid image recording apparatus can be divided by the types of its recording head into those of an ink jet type, wire dot type, thermal type, laser beam type, and others.
Of those types mentioned above, the ink jet type has, particularly, the advantage that a highly precise image can be recorded at high speeds because with this type, ink is discharged from its recording head onto a recording medium, and that not only the recording is performed with less noise but a color image is easily recorded with the use of multicolor ink because the non-impact system is adopted for this type.
Particularly for the ink jet type image recording apparatus among those image recording apparatuses mentioned above, fixating means for expediting the fixation of the recorded image is provided in consideration of the recording on a recording medium having a slow ink fixation rate such as an OHP sheet.
FIGS. 1A to 1G are views schematically showing the operational principle of the recording head for a preferred ink jet recording apparatus.
In FIGS. 1A to 1G, there is formed in a recording head 50 an ink pass or passage 51 which is connected to a liquid chamber (not shown) in which ink is temporarily stored, and the leading end of the aforesaid ink pass 51 is opened to the face plane (the plane facing the recording medium with a predetermined space) 52 of the recording head 50 to form a discharging port 53.
In the aforesaid ink pass 51, ink (recording liquid) 54 is filled. Also, on the inner wall in the vicinity of the discharging port 54 of the aforesaid ink pass 51, a heater (electrothermal converter) 55 is provided.
The aforesaid heater 55 is connected to an electrode 56 for energizing.
FIG. 1A illustrates a state before the heater is energized. When the heater 55 is energized in response to an applied signal, the aforesaid heater 55 is caused to generate heat, so that ink 54 in the vicinity of the area in contact with the heater is rapidly heated (FIG. 1B).
By this heating, a rapid vaporization occurs in the ink 54 (FIG. 1C), and a bubble 57 is formed.
By the growth (expansion) of this bubble 57, ink is pressurized to cause it to be expansively projected from the discharging port 53 (FIG. 1D).
If the boundary between the bubble 57 and ink 54 is cooled at the time of the ink having been expansively projected sufficiently from the discharging port 53 (FIG. 1E), the expansively projected ink is discharged from the discharging port 53 as an ink droplet 58 and at the same time, the expanded bubble 57 is contracted (FIG. 1F).
FIG. 1G illustrates a state that an ink droplet has been formed in an appropriate amount for flight towards the recording medium and that the bubble in the ink pass 51 has disappeared simultaneously.
Thus, the ink droplet is caused to adhere to the recording medium to form a dot (perform a recording), and further the next discharging operation (recording operation) is prepared.
FIG. 2 is a partially perspective view schematically showing the discharging unit (recording unit) 40 of the aforesaid recording head 10.
In FIG. 2, a plurality of discharging ports 42 are formed at predetermined pitches on the discharging port surface 41 opposite to the recording medium 12 with a predetermined space (for example, approximately 0.5-2.0) between them, and an electrothermal converter (exothermic resistor and the like) 45 is arranged along the wall of each liquid pass or passage 44 which communicatively connects a common liquid chamber 43 and each discharging port 42.
FIG. 3 is a partially perspective view schematically showing the structure of the ink discharging unit of the recording head 10 in FIG. 2.
In FIG. 3, a plurality of electrothermal converters 22 and the wirings with respect thereto are formed by the same processes as fabricating semiconductors (thin film formation method or the like) on the substrate 21 of the recording head 10 through a thin film layer 23.
The aforesaid electrothermal converters 22 are arranged as shown in FIG. 3 at the positions with respect to the discharging ports and liquid passages which will be described later.
To the aforesaid substrate 21 (on the thin film 23 of the substrate 21), there is joined a liquid pass or passage formation member 24 having a plurality of liquid pass or passage walls 24A produced in parallel at the bottom face thereof at predetermined intervals.
Further, a ceiling plate 25 is joined to the upper face of the aforesaid liquid pass formation member 24.
Liquid passes or passages 26 are produced between each of the aforesaid liquid pass walls 24A, and the aforesaid liquid pass formation member 24 is joined in such a way that each of the aforesaid electrothermal converters 22 is positioned with a positional relationship in each of the liquid passes 26 so as to arrange each of them at a predetermined position therein.
Each of the aforesaid liquid pass walls 24A has a predetermined length, and the rear end of each liquid pass 26 is comunicatively connected with the common liquid chamber 27 produced between the aforesaid liquid pass formation member 24 and the substrate 21 (or the thin film 23).
Meanwhile, the other end (the leading end) of each liquid pass 26 is opened as a discharging port 29 respectively in the discharging port surface (face plane) 28 of the recording head 10.
Thus, the ink jet recording head is constructed to enable ink in the liquid pass 26 to be film boiled by the heat which is generated by energizing (by applying pulse voltage to) the exothermic resistor and the like constituting the electrothermal converter 22 thereby to cause the ink droplet to be discharged from the discharging port 29 by the variation of pressure thus created at that time.
According to the recording method set forth above, the fixing capability of the ink which has adhered to the recording medium depends greatly on the water absorptivity and other characteristics of the aforesaid recording medium.
For example, the fixing capability of ink differs when the aforesaid recording medium is an ordinary paper or some other usual recording sheet as opposed to when an OHP (overhead projector) sheet whose water absorptivity is inferior is used as a recording medium.
In other words, in the case of the ordinary sheet used, the ink is rapidly absorbed and there is no need for a particular fixing means for a recording without any difficulty. In the case of the OHP sheet, however, it is necessary to give a certain time (several minutes, for example) for the fixation of ink due to its inferior water absorptivity or it may be required to use a heating means or some other means to dry ink quickly.
Under the circumstances, there has been proposed an installation of a heat-drying type fixater particularly for an ink jet recording apparatus.
FIG. 4 is a schematic side view showing a structural example of the fixing means for a conventional image recording apparatus.
In FIG. 4, the fixing means for the conventional image recording apparatus is structured with the arrangement of a heater 61 for the ink fixation on the reverse side of a platen 62 of its recording unit to heat the recorded recording medium 67 by the aforesaid heater for the ink fixation, so that the recorded image is not smeared even if the recording surface is touched by a finger at the time of the recording medium P having been exhausted.
In the conventional recording apparatus, however, there exist the technical problems given below.
i) In a recording apparatus in which a fixater is incorporated, the fixater is permanently installed for an OHP sheet for which the apparatus is not used often, leading to the larger size of the apparatus, and the increase of the manufacturing cost and power consumption. Therefore, for those users who do not use an OHP sheet, this type of fixater is redundant.
ii) For the conventional recording apparatus using a detachable fixater, it is necessary for the user to attach the fixater to or detach it from the apparatus depending on whether an ordinary paper is used or an OHP sheet is used for recording, and the user finds it rather troublesome in handling the fixater each time as required.
iii) Sometimes a user wishes to use his apparatus for recording an OHP sheet even when he does not have a fixater which is available as an option to his apparatus. In such a case, it is difficult for him to cope with the situation.
Also, there are problems such as given below if a paper is handled for recording in a state where the fixater is installed in the apparatus.
A) Deterioration of paper quality and degradation of image quality.
B) Sheet jamming and other troubles occurring in the fixater when the paper is fed due to the different properties of the sheet and OHP sheet for transportability.
C) Further, in a structure such as shown in FIG. 4, the ink recorded on an OHP sheet is evaporated by heat of the heater 61, and the discharging port 66a of the recording head 66 may sometimes be moisturized when exposed to the water vapor emitted therefrom, lowering the recording quality or sometimes, causing drawback such as a disabled recording.
Furthermore, in an ink jet recording apparatus with a conventional fixater mounted therein, the driving condition of the fixater, conveying velocity of the recording medium, the amount of ink to be discharged and other prerequisites are defined to equalize the drying effect of ink fixation on the recorded recording medium, thus making it impossible to provide a compact and inexpensive ink jet recording apparatus, being also capable of drying the rear portion of the recording medium sufficiently at the same time.